The present invention relates to an apparatus for detecting a level of liquid in a liquid storage tank, and provides a float type liquid level meter comprising a connecting lever which has a structure to suppress a fluctuation of a liquid level signal.
In a conventional float type liquid level meter, a connecting lever connecting a float and an apparatus for detecting buoyancy is comprised of a solid rod of small diameter, having a lighter weight than the float and of sufficient strength to hold the float, aiming only to transmit changes in weight of the float and which changes depend on a liquid level to the apparatus for detecting buoyancy. Therefore, such methods to provide a countermeasure with elements other than a connecting lever itself as a method to insert the connecting lever into a guide tube without any contact and a method to furnish supporting arms, extended from a float toward an inside wall of a liquid storage tank etc., are used as a method to suppress and moderate effects of disturbance which are caused with a bending stress to the connecting lever by buoyancy, or with a lateral oscillation by liquid flow. Several float type liquid level meters according to prior art are exemplified in the publication, such as, Japanese Patent Application Laid-Open No. 57-10417.
An example of the prior art using a tubular rod as a connecting lever to transmit a change of liquid level is disclosed in the U.S. Pat. No. 4,646,796, but a float to detect a liquid level and the connecting rod move concurrently with a magnetic connection and the float and the connecting rod are not connected directly. Therefore, the U.S. Pat. No. 4,646,796 is different in composition of a liquid level meter from the present invention, in which a float type liquid level meter comprising a float, an apparatus to detect buoyancy of the float and to convert the buoyancy to a liquid level, and a connecting rod which connects the float and the apparatus to detect buoyancy is disclosed.
The prior art described above considers a disturbance caused by buoyancy and liquid flow but not that from an external vibration effected directly to the liquid level meter itself. Consequently, when a vibration is caused at a place where the liquid level meter is installed, the vibration is transmitted to the liquid level meter itself and a phenomenon causing the fluctuation of an output signal from the liquid level meter is generated in spite of the liquid level itself being kept stable.
As a countermeasure for the phenomenon, in the case of a liquid level regulating system in which a regulating valve is operated with a regulator which intakes an output signal from a liquid level meter, a method for using the regulator having a large time lag element is adopted in order to prevent a fluctuation of the output signal of the liquid level meter from effecting directly the liquid level regulating system. But, if the fluctuation of the output signal of the liquid level meter is suppressed, it is possible to use a regulator having a small time lag element and to respond quickly to a change of liquid level, and consequently, a performance of the liquid level regulating system is improved.